Temperature dependence of dislocation bias factors in metals

Recently, it has been shown that edge dislocations are not stable sinks for vacancies. Trapping and detrapping of vacancies occur as a thermally-activated process. In this paper, the temperature dependence of vacancy absorption coefficient of edge dislocations under irradiation was calculated by using rate equations in Fe and Ni. The temperature dependence was almost the same in both Fe and Ni and did not depend on the damage rate between 10⁻¹⁰ dpa/s and 10⁻⁶ dpa/s. At low temperatures such as room temperature, the coefficient was low and with increasing irradiation temperatures, it had a peak (500 K) and decreased.     

HRTEM study of oxide nanoparticles in K3-ODS ferritic steel developed for radiation tolerance

Crystal and interfacial structures of oxide nanoparticles and radiation damage in 16Cr-4.5Al-0.3Ti-2W-0.37 Y₂O₃ ODS ferritic steel have been examined using high-resolution transmission electron microscopy (HRTEM) techniques. Oxide nanoparticles with a complex-oxide core and an amorphous shell were frequently observed. The crystal structure of complex-oxide core is identified to be mainly monoclinic Y₄Al₂O₉ (YAM) oxide compound. Orientation relationships between the oxide and the matrix are found to be dependent on the particle size. Large particles (>20 nm) tend to be incoherent and have a spherical shape, whereas small particles (<10 nm) tend to be coherent or semi-coherent and have a faceted interface. The observations of partially amorphous nanoparticles and multiple crystalline domains formed within a nanoparticle lead us to propose a three-stage mechanism to rationalize the formation of oxide nanoparticles containing core/shell structures in as-fabricated ODS steels. Effects of nanoparticle size and density on cavity formation induced by (Fe⁸⁺ + He⁺) dual-beam irradiation are briefly addressed.     

Dose and Temperature Dependence of Void Swelling in Electron Irradiated Stainless Steel

In a high voltage electron microscope, solution treated Type 316 stainless steel was electron-irradiated at temperatures in the range of 370–630°C to a dose of about 30 dpa. The swelling (ΔV/V) induced by the irradiation beyond about 5 dpa is well described by an empirical equation, ΔV/V=A(dpa) ⁿ , under constant void and dislocation densities. With increasing irradiation temperature, the fluence exponent n increases and the pre-exponent term A decreases. At 550°C irradiation, the fluence exponent takes the value of 1.5 due to the diffusion-limited void growth. The value of n larger than 1.5 at higher temperature (>550°C) is attributable to the surface reaction-limited void growth. The smaller value of n for the low temperature (?500°C) irradiation appears to arise from the dislocation assisted vacancy diffusion. The peak swelling temperature of the specimen irradiated to 30 dpa is about 570°C, which shifts to a higher temperature with increase in electron dose.     

Resistance to void formation of Cu-Ni alloys

Cu-Ni alloys were found by Brimhall and Kissinger to be void-resistant in a low-dose neutron irradiation experiment. This fact was investigated at much higher damage doses by means of irradiations at various temperatures between 300°C and 600°C with Ni⁺, Cu⁺ or C⁺ at 0.1 MeV, or Ni⁶⁺ at 46.5 MeV. Only the 2% Cu and 2% Ni alloys showed voidage whilst those containing 20, 50, 80% Ni were found to be completely free from voids at atom displacement levels well in excess of 30 dpa. It is proposed that fine-scale clusters having a different composition from the solid-solution matrix may be acting as traps for displaced interstitials and vacancies, so inhibiting vacancy agglomeration into voids.     

Irradiation damage in proton irradiated palladium-iron solid solutions

Transmission electron microscopy was used to investigate the irradiation damage, in particular irradiation induced precipitation (IIP), in Pd-base alloys containing 2, 8, 12 and 18 at % Fe. The specimens were irradiated mainly using 400 keV protons at a current density of 0.16 μA/mm² over the temperature range 110 to 750°C. A few samples containing 2 and 8% Fe were also irradiated using 3 MeV NiP⁺ ions. The irradiation microstructure of the proton irradiated alloys consists of dislocation loops over the temperature range 110 to 550°C and voids up to 650°C in all the alloys. IIP of Pd₃Fe was observed only in the Pd-18% Fe alloy between 110 and 500°C, irradiated to a dose of 0.9 dpa. Pd₃Fe was associated with dislocation loops, voids and grain boundaries. IIP was not observed in the Pd-2,8 and 12% Fe alloys proton irradiated to the same dose, nor to a higher dose of 1.5 dpa. It was also not observed in the 2 and 8% Fe alloys irradiated at 600 and 700°C by 3 MeV Ni⁺ ions.The absence of IIP in the more dilute alloys is attributed to the fast back diffusion of Fe atoms, which is due to the high mobility of vacancies in these alloys. This causes the Fe concentration at the sinks to remain below the solubility limit. Therefore, even though Fe is an undersized solute, the size effect alone is not sufficient for the production of IIP at point defect sinks in most Pd-Fe alloys. It is proposed that IIP can occur only when the alloy concentration is high enough to minimize the rate of back diffusion, which depends not only on the vacancy mobility but also on the concentration gradient near point defect sinks.     

Thermal desorption of helium from defects in nickel

Helium atoms, introduced into materials by helium plasma or generated by the (n, α) nuclear reaction, have a strong tendency to accumulate at trapping sites such as vacancy clusters and dislocations. In this paper, the effects of dislocations, single vacancies and vacancy clusters on the retention and desorption of helium atoms in nickel were studied. Low energy (0.1-0.15 keV) helium atoms were implanted in nickel with vacancies or dislocations without causing any displacement damage. He atoms, interstitial-type dislocation loops, and vacancy clusters were also introduced with irradiation damage by 5.0 keV helium ions. Helium thermal desorption peaks from dislocations, helium-vacancy clusters and helium bubbles were obtained by thermal desorption spectroscopy at 940 K, in the range from 900 to 1370 K, and at 1500 K, respectively. In addition, a thermally quasi-stable state was found for helium-vacancy clusters.     

Microstructural evolution in nickel alloy C-276 after Ar ion irradiation

Irradiation damage in nickel alloy C-276 irradiated by 115 keV argon ions at room temperature with irradiation doses from 0.28 to 82.5 dpa has been investigated by transmission electron microscopy. Nano-scale black spot damage appeared at a dose higher than 0.83 dpa. Large interstitial-type dislocation loops were observed at the dose of 8.25 dpa. Both the density of dislocation loops and the density of network dislocations grew significantly with the increase of irradiation dose. However, the density of network dislocations declined at the dose of 27.5 dpa. But the total of dislocation density (density of dislocation lines plus density of dislocation loops) kept increasing and no signs of saturation were seen in the dose range explored. The results showed that the nickel alloy C-276 had good performance in delaying the development of black spots, dislocations and dislocation loops. However, original grains have formed into subgrains at the dose of 82.5 dpa, meaning that the grains in C-276 lost its structural integrity at doses higher than 82.5 dpa.     

氦离子辐照烧结碳化硅损伤效应研究

利用中国科学院近代物理研究所320 kV高压平台提供的氦离子辐照烧结碳化硅,辐照温度从室温到1 000 ℃,辐照注量为1015~1017 cm-2。辐照完成后,进行退火处理,然后开展透射电子显微镜、拉曼光谱、纳米硬度和热导率测试。研究发现,烧结碳化硅中氦泡形核阈值注量低于单晶碳化硅。同时,氦泡形貌和尺寸与辐照温度、退火温度有关。另外,对辐照产生的晶格缺陷、元素偏析进行了研究。结果表明,辐照产生了大量的缺陷团簇,同时氦泡生长也会发射间隙子,在氦泡周围形成间隙型位错环。在晶界处,容易发生碳原子聚集。辐照导致材料先发生硬化而后发生软化,且热导率降低。     

Ion irradiation damage effects in δ-phase Y6W1O12

Polycrystalline Y₆W₁O₁₂ samples were irradiated with 280 keV Kr²⁺ ions to fluences up to 2 × 10²⁰ ions/m² at cryogenic temperature (100 K). Ion irradiation damage effects in these samples were examined using grazing incidence X-ray diffraction (GIXRD) and cross-sectional transmission electron microscopy (TEM). The pristine Y₆W₁O₁₂ possesses rhombohedral symmetry (structure known as the δ-phase), which is closely related to cubic fluorite structure. GIXRD and TEM observations revealed that the irradiated Y₆W₁O₁₂ experiences an ordered rhombohedral to disordered cubic fluorite transformation by a displacement damage dose of ∼12 displacements per atom (dpa). At the highest experimental dose of ∼50 dpa, the uppermost irradiated region was found to be partially amorphous while the buried damage region was found to contain the same fluorite structure as observed at lower dose.     

The effect of neutron irradiation on mechanical properties of YAG laser weldments using previously irradiated material

The objective of this study is to make clear the effect of neutron irradiation on mechanical properties of laser weldments using irradiated material. This estimation is necessary for the application to joining coolant piping of the ITER blanket. Irradiation testing was performed at Japan Material Testing Reactor (JMTR). On the irradiation condition for weldments using irradiated material, fast neutron fluence was 1.4 × 10²⁴ n/m², which corresponds to a displacement damage rate of 0.26 displacement per atom (dpa) and irradiation temperature 200 °C. The results of this study show that tensile properties of all weldments changed into that of base material by the effect of neutron irradiation. The results of hardness tests show that irradiation hardening at an irradiation damage dose of 0.3 dpa is almost same as that at irradiation damage 0.6 dpa. It is concluded that irradiated weldments using irradiated material were moved toward irradiated base material on tensile and hardness properties up to 0.6 dpa. On the other hand, tensile properties of base material were changed by the effect of neutron irradiation up to about 0.3 dpa, and with much less change from 0.3 dpa to 0.6 dpa. It is inferred that the effect of neutron irradiation of SS316LN-IG almost saturated up to 0.3 dpa.     

Ab initio simulation of yttrium oxide nanocluster formation on fcc Fe lattice

Using results of density functional theory (DFT) calculations the first attempt towards the understanding of Y₂O₃ particles formation in oxide dispersed strengthened (ODS) ferritic-martensitic steels was performed. The present work includes modeling of single defects (O impurity atom, Fe vacancy and Y substitute atom), interaction between substituted Y atoms, Y-Fe vacancy pairs and oxygen impurity atoms in the iron matrix. The calculations have showed the repulsive interaction between the two Y substitute atoms at any separation distances that might mean that the oxygen atoms or O atoms with vacancies are required to form binding between atoms in the yttrium oxide nanoclusters.     

The disordering of Zr3Al by 1 MeV electron irradiation

The effect of 1 MeV electron radiation on the L1₂ ordered intermetallic compound, Zr₃Al, has been studied over the temperature range 130–775 K, using a high voltage electron microscope. At temperatures in the range 130–375 K, complete disorder was produced by irradiation to a dose of approximately one displacement per atom (dpa), independent of damage rate over the range 5 × 10^?4 to 5 × 10^?3 dpa/s. After irradiation to a few dpa at higher temperatures, 575–775 K, a steady-state was established which was characterized in part by an intermediate degree of long-range order which increased with irradiation temperature. By comparison with published results from ion irradiation experiments, it appears that the number of atomic displacements to cause complete disordering at low temperatures is independent of the nature of the damage events. At the higher temperatures, neither dislocation loops, dislocation networks nor voids were observed. Generally, the crystalline perfection was markedly reduced at all temperatures by irradiation to doses exceeding a few dpa.     

Effect of Zirconium Addition to Austenitic Stainless Steels on Suppression of Radiation Induced Chromium Segregation at Grain Boundaries under Ion Irradiation

The effect of Zr addition to austenitic stainless steels on the suppression of radiation induced Cr segregation at grain boundaries under 400 keV He⁺ irradiation was studied. Type 316L stainless steel and steels with addition of 0.07, 0.21 or 0.41 mass% Zr were kept at 1,423K for 30 min, and then they were quenched into the water. Irradiation was done at 773K with the dose rate of 2.4×10^?4dpa/s. The total dose was 0.85 or 3.4dpa. After irradiation, profiles of Cr concentration across the grain boundaries were measured using an analytical electron microscope with 1 nm beam diameter. Concentration of Cr at the grain boundary is decreased by radiation induced segregation. However, it increased with the addition of Zr, and the Cr segregation is almost completely suppressed when Zr is added more than 0.21 mass%.

The effect of Zr addition on suppression of Cr segregation was analyzed focussing on the interaction between dissolved Zr atoms and point defects. The effect is based on vacancy trapping by the Zr atom, and the extent to which it suppresses Cr segregation can be empirically evaluated using a radiation induced segregation model by changing the effective vacancy migration energy.     

Creep and microstructural changes in dispersion hardened Ni-20% Cr-1% ThO2 during proton irradiation

Irradiation creep and microstructural changes were studied at 573 K in a 20% cold worked Ni-20% Cr-1% ThO₂ alloy under 6.2 MeV proton irradiation. The irradiation creep strength was in the range of values found for FeCrNi alloys and for solution- and precipitation-hardened nickel alloys. Displacement doses up to 0.35 dpa increase the dislocation density in the cold worked specimens but have no observable effect on the dispersed ThO₂ particles.Resistivity changes were observed in annealed as well as in cold worked specimens during thermal aging and to a much higher degree during irradiation. Transmission electron microscopy studies were inconclusive whether this was caused by short range ordering or by precipitation of a second phase in the NiCr system.     

Ion beam radiation effects in monazite

Monazite is a potential matrix for conditioning minor actinides arising from spent fuel reprocessing. The matrix behavior under irradiation must be investigated to ensure long-term containment performance. Monazite compounds were irradiated by gold and helium ions to simulate the consequences of alpha decay. This article describes the effects of such irradiation on the structural and macroscopic properties (density and hardness) of monazites LaPO₄ and La_0.73Ce_0.27PO₄. Irradiation by gold ions results in major changes in the material properties. At a damage level of 6.7 dpa, monazite exhibits volume expansion of about 8.1%, a 59% drop in hardness, and structure amorphization, although Raman spectroscopy analysis shows that the phosphate-oxygen bond is unaffected. Conversely, no change in the properties of these compounds was observed after He ion implantation. These results indicate that ballistic effects predominate in the studied dose range.     

Neutron irradiation hardening and microstructure changes in Fe-Mn binary alloys

Irradiation hardening and microstructure changes in Fe-Mn binary alloys were investigated after neutron irradiation at 290 °C and up to 0.13 dpa. Significant irradiation hardening comparable to that of Fe-1 at.%Cu alloy was observed in Fe-1 at.%Mn alloy. Manganese increases the number density of dislocation loops, which contributed to the observed irradiation hardening. Manganese serves as a nucleus of the loop by trapping interstitial atoms and clusters, preventing 1D motion of the loops.     

Void Swelling of Solution-Annealed Type 316 Stainless Steel under Long Time Proton Irradiation

Solution-annealed type 316 stainless steel was irradiated by 150 keV proton to a dose of about 6 dpa at the irradiation temperature ranging 450–700°C. To examine the effect of aging during irradiation, the present proton irradiation was carried out for about 25 h at a low dose rate of 7×10–^?5dpa/s. The specimens without He preinjection showed much smaller void swelling than those preinjected with He to the content of 10 at.ppm. Similarly to the case of neutron irradiations, the void swelling in the He preinjected specimens showed the temperature dependence with double peaks, and the peak swelling temperatures were about 550 and 650°C. In these specimens with He preinjection. void number density decreased and average void diameter increased with the increase of irradiation temperature in the range of 450–600°C, but these trends were reversed between 600 and 650°C. The volume of the grain boudary M₂₃C6 precipitates increased with the increase of irradiation temperature from 600 to 700°C, and it was concluded that the decrease of soluble carbon due to the precipitation of M₂₃C6 caused the second swelling peak at 650°C.     

The effect of vacancy created by ion irradiation on the ordering of FePt: A first-principle study

Ion irradiation has been used to promote ordering processes and to modify the magnetic properties of magnetic thin films. The major reason for ion irradiation reducing the ordering temperature is the introduction of a number of vacancies. The vacancy and its influence on the ordering temperature and magnetic properties in L1₀ ordered FePt are investigated by first-principle simulation. The vacancy formation energy for Fe and Pt in FePt alloy are 1.45 and 2.25 eV respectively. The calculated order-disorder transition temperature of Fe₅₀Pt₅₀ is 1680 K. The order-disorder transition temperatures for Fe vacancy and Pt vacancy models are about 50 K and 200 K lower than that of the stoichiometric Fe₅₀Pt₅₀ alloy respectively. The results suggested that the vacancy in FePt alloy favors the ordering process. The saturation magnetization of stoichiometric L1₀ FePt is 1070 emu/cc and these of Fe and Pt vacancy are 1027 and 1075 emu/cc, respectively.     

Generation of c-component edge dislocations in α-zirconium during neutron irradiation - An atomistic study

The nucleation and multiplication of c-component edge dislocation segments during neutron irradiation in zirconium and its alloys is known to have important consequences to their in-reactor deformation behavior. Although there are ample experimental observations showing the close correlation between the edge-type and the screw-type of c-dislocations, the relation between them is unclear. In this paper, we performed atomistic study of the interaction between a [0 0 0 1] screw dislocation and a vacancy cluster in the form of a platelet on the basal plane. The local minimum-energy configuration was obtained using the conjugate-gradient method, with boundary relaxation achieved via a modified Green’s function method. Under stress-free conditions, the vacancy clusters maintained their cavity nature. With a [0 0 0 1] screw dislocation in the close neighborhood, vacancy clusters containing more than 23 vacancies collapse into faulted vacancy loops. Interaction at even closer range leads to the disappearance of the vacancy cluster and the development of an edge component on the originally straight screw dislocation in the form of a helical line. The implications of these findings are discussed in relation to the experimentally observed behavior of growth acceleration in zirconium and its alloys.